Self-fading color adhesive

ABSTRACT

This invention relates to a sprayable adhesive that, when applied to a substrate, exhibits a color that confirms where it has been applied and then fades upon drying.

FIELD OF THE INVENTION

This invention relates to an adhesive that, when applied to a substrate,exhibits a color that confirms where it has been applied and then fadesupon drying.

BACKGROUND ART

For the purpose of confirming the area coated and the weight of theadhesive applied when adhesives are sprayed, adhesives colored bypigments or dyes have been used. Such adhesives do not fade or changecolor after spraying and drying, and are consequently undesirable formany applications.

The present invention provides an adhesive, preferably an aerosoladhesive, that, immediately after application, exhibits a color whichallows confirmation of the area coated and the weight of the adhesiveapplied. The color of the adhesive subsequently fades to clear upondrying.

SUMMARY OF THE INVENTION

The present invention relates to a self-fading color adhesive. Theself-fading color adhesive shows a color immediately after spraying andsaid color fades with the passage of time. In general it can be usedadvantageously where it is desirable to see the portion of the substrateinitially treated with adhesive, but where it would be undesirable forthe final adhesive to have color. For example, in applications involvingthin, clear or lightly colored substrates, it may be undesirable to havethe adhesive permanently colored, since the adhesive would permanentlydistort the color of the substrate.

DETAILED DESCRIPTION OF THE INVENTION

The invention is preferably directed towards incorporating a colorchanging acid-base indicator into sprayable adhesives. Morespecifically, the self-fading color adhesive of the present inventioncomprises the following components: (a) clear or slightly coloredorganic solvent type adhesive, (b) basic material which readilyvolatilizes at ambient temperatures, (c) acid-base indictor which iscolored in basic environment and turns clear in non-basic environment,and preferably (d) spraying agent.

The invention is not intended to be limited to specific adhesivecomposition. The non-volatile adhesive components can be selected from awide variety of adhesive components commonly employed in adhesivesincluding polymers of acrylic esters or partially crosslinked acrylicesters and elastomeric adhesives including partially crosslinked orsoluble styrene-butadiene rubber, butyl rubber, thermoplastic blockcopolymers such as styrene-isoprene-styrene or styrene-butadiene-styreneblock copolymers, polychloroprene rubber, natural rubber andbutadiene-acrylonitrile rubber. Other classes of adhesives such aspolyvinyl chloride, polyvinylacetate, polyvinylalcohol andpolyvinylpyrrolidone also form suitable sprayable adhesives. Theadhesive can also include tackifiers, such as polyterpene resins andhydrogenated rosin esters. A preferred acrylic ester is a crosslinkedisooctyl acrylate and acrylic acid copolymer which can be made by themethod described in U.S. Pat. No. 3,578,622, Example 1.

Preferred tackifiers are hydrogenated rosin esters such as Estergum H,available from Arakawa Chemical Co., Ltd., and Pentalyn H and Foral 105both available from Hercules Co. Other suitable tackifiers are terpenephenolic resins such as SP-560 resin available from Schenectedy ChemicalCo. and hydrocarbon resins such as Arkon P115 resin available fromArakawa Company (Japan). The tackifier could also be selected fromphenolic resins, and plasticizers such as dioctylphthalate (DOP) anddioctylsebacate (DOS). In the present invention, the non-volatileadhesive components and tackifiers can be used alone or in combinationof two or more.

The organic solvents in the present invention may be selected from aproper quantity of known solvents which readily volatilize at normal(ambient) temperature, such as n-hexane, n-heptane, methylethylketone,isohexane, methanol, ethanol and

Desirable basic materials which readily volatilize at ambienttemperatures for use in the present invention, include aminoalcoholssuch as alkylamines such as ethylamine, diethylamine, methylamine,dimethylamine, triethylamine; ethyleneamines such as ethyleneamine,diethyleneamine; nitrogen heterocyclic compounds such as morpholine, andammonia. The selection of the kind and the amount of base material usedenables control of the time until fading of the color after spraying.Suitable basic materials which readily volatilize at ambienttemperatures, typically have a vapor pressure higher than about 10 mmHgat 20° C.

The acid-base indicators used in the present invention, are colored inbasic condition and fade to clear in non-basic condition. Acid-baseindicators which are colored on alkali pH side (pH >7) and turn clear onacidic pH side.(i.e., pH <7) are preferable. Typically, the preferredacid-base indicators are colored at pH between about 9 and 10 and turnclear at pH between about 6 and 8. More exactly, the following compoundsare recited as preferred acid-base indicators:

dinitrophenol(2,5-dinitrophenol),

heptamethoxy red, p-nitrophenol, pinachrome,

m-nitrophenol, quinolein blue (cyanine),

Ethyl-bis(2,4-dinitrophenyl)-acetate,

p-cresolphthalein, phenolphthalein,

o-cresolphthalein, thymolphthalein,

bromophenol purple, methyl green,

nitroamine, basic fuchsine, crystal violet,

trinitrobenzoic acid, 1,3,5-trinitrobenzene,

acid fuchsine.

With the suitable selection of said acid-base indicators, it is possibleto realize any color. Additionally, combinations of two or moreindicators may be used.

Preferred spraying agents in the present invention are aerosol agentswhich include liquified propellents such as dimethylether (DME) andliquid petroleum gas (LPG) and liquified propane, butane and iso-butane,and liquified fluorocarbons and chlorofluorocarbons. Other suitableaerosol agents may be selected from compressed gasses such as carbondioxide and nitrogen.

The use of a self-fading color adhesive in the present invention enablesconfirmation of the coating area and weight of the adhesive easily. Inaddition, because the adhesive turns almost clear after drying, theadhesive can be applied widely in consideration of its externalappearance, as compared with conventional colored adhesives. Preferably,the adhesive is filled in a container, such as an aerosol can, so thatthe adhesive and indicator properties remain preserved for a long time.Therefore, the adhesive in the present invention has a high industrialvalue.

Further, adhesives within the scope of the present invention may exhibitsomewhat different adhesive properties when exposed to basic andnon-basic conditions. Utilizing this property, the adhesive can be usedboth for permanent adhesion and for temporary adhesion. For example,when the adhesive of Example 1 described below is used to adhere paper,the adhesive exhibits a strong adhesion to paper when the paper attachedjust after spraying the adhesive (i.e. when the adhesive is stillcolored). In contrast, when the paper is attached after fading of thecolor, the paper can be exfoliated without damage.

Although the present invention has been described primarily withreference to an aerosol spray, the invention can also be employed bycoating the self fading adhesive onto a substrate. In such case,essentially the same formulations can be used but without the sprayingagent.

EXAMPLES 1-3

The acrylic polymers, resins, and solvents shown in Tables 1 to 3 weremixed by a stirrer with a high shear dissolver type propeller, and werestirred uniformly to disperse the polymers finely (A). Acid-baseindicators were dissolved in acetone completely and basic materials werefurther added (B). Then, (A) and (B) were mixed and stirred completelyto be uniform(C). (C) was introduced into an aerosol can and afterinsertion of a valve, a spraying agent was filled into the can.

EXAMPLE 4

Polysar S-1018 rubber, which is a styrene butadiene rubber crosslinkedwith di-vinyl benzene, was passed through a two-roll type rubber mixerthree times and then was formed into small chips. The chips were addedinto N-hexane and cyclohexane and Estergum H was further added. Themixture was stirred by a stirrer with a high shear dissolver typepropeller to obtain uniform dispersed product (A). Phenolphthalein wasdissolved into ethanol completely and ammonia water and morpholine werefurther added (B). (A) and (B) were mixed and stirred to be uniform (C).(C) was introduced into an aerosol can and after insertion of a valve,liquid petroleum gas (LPG) and dimethylether (DME) were filled into thecan.

The adhesive composites were attached by a spray method on a steelsheet, and the coloring condition was observed with the passage of time.At the same time, said adhesives were sprayed on a steel sheet andcanvas was attached thereto. Then the adhesive strength was measured byan 180 degree exfoliation test.

The results and the visible observation results were shown as follows.

                  TABLE 1                                                         ______________________________________                                                          Working Example                                             Composition         1        2                                                ______________________________________                                        Crosslinked isoacrylate 1)                                                                        6.62%    6.62%                                            acrylic acid copolymer                                                        Estergum H hydrogenated 2)                                                                        4.12%    4.12%                                            rosin ester                                                                   n-Hexane            59.25%   59.25%                                           Acetone             3.18%    3.18%                                            Ethylbis (2,4-dinitrophenyl)-                                                                     0.11%    0.11%                                            acetate                                                                       Ammonia water. 28%  0.39%    0.39%                                            Morpholine          0.10%       0%                                            DME (spraying agent)                                                                              26.23%   26.33%                                                               100.00%  100.00%                                          ______________________________________                                         Notes:                                                                        1) As described in U.S. Pat. No. 3,578,622, Example 1.                        2) Manufactured by Arakawa Chemical Co.                                  

                  TABLE 2                                                         ______________________________________                                                           Working Example                                            Composition        3                                                          ______________________________________                                        Microsphere of isoacrylate                                                                       5.41%                                                      acrylic ester polymer 3)                                                      i-Hexane           20.08%                                                     Acetone            17.48%                                                     Ethyl acetate      1.34%                                                      Ethylbis(2,4-dinitrophenyl)-                                                                     0.17%                                                      acetate                                                                       Ammonia water, aq 28%                                                                            0.55%                                                      Morpholine         0.42%                                                      i-Butane (spraying agent)                                                                        54.55%                                                                        100.00%                                                    ______________________________________                                         Notes: 3) As described in U.S. Pat. No. 4,994,322, Table 2, Example 2.   

                  TABLE 3                                                         ______________________________________                                                             Working Example                                          Composition          4                                                        ______________________________________                                        Polysar S-1018, 4)   9.63%                                                    Partial crosslinked SBR                                                       Estergum H, hydrogenated 2)                                                                        14.64%                                                   rosin ester                                                                   n-Hexane             32.34%                                                   Cyclohexane          10.81%                                                   Ethanol              1.68%                                                    Phenolphthalein      0.12%                                                    Ammonia water, aq 28%                                                                              0.79%                                                    Morpholine           0.39%                                                    LPG (spraying agent) 19.73%                                                   DME (spraying agent) 9.87%                                                                         100.00%                                                  ______________________________________                                         Notes:                                                                        2) Manufactured by Arakawa Chemical Co.                                       4) Manufactured by the Canada based Polysar Co.                          

                  TABLE 4                                                         ______________________________________                                                    Working Example                                                   Composition  1         2       3       4                                      ______________________________________                                        Color of adhesive                                                                          blue      blue    blue    pink                                   in spraying                                                                   Color after drying                                                                         white     white   white   slight-                                             or        or      or      ly                                                  clear     clear   clear   brown                                  Time until turning                                                                         5         0.5     10      1                                      clear (minute)                                                                Adhesive strength                                                                          0.6       0.6     0.3     2.2                                    (kg/25 mm)                                                                    canvas/steel                                                                  180 degree                                                                    exfoliation                                                                   ______________________________________                                    

We claim:
 1. A sprayable, self-fading color adhesive comprising thefollowing four components:a) clear or slightly colored adhesivedissolved in an organic solvent, b) basic material which readilyvolatilizes at ambient temperatures, c) acid-base indicator which iscolored in a basic environment and fades to clear upon drying, and (d)spraying agent.
 2. An adhesive according to claim 1 wherein said basicmaterial is selected from the group consisting of aminoalcohols,alkylamines, ethyleneamines, nitrogen-containing heterocyclic compounds,and ammonia.
 3. An adhesive according to claim 1 wherein said basicmaterial has a vapor pressure higher than about 10 mmHg at 20° C.
 4. Anadhesive according to claim 1 wherein said acid-base indicator isselected from the group consisting of:dinitrophenol(2,5-dinitrophenol),heptamethoxy red, p-nitrophenol, pinachrome, m-nitrophenol, quinoleinblue (cyanine), Ethyl-bis(2,4-dinitrophenyl)-acetate, p-cresolphthalein,phenolphthalein, o-cresolphthalein, thymolphthalein, bromophenol purple,methyl green, nitroamine, basic fuchsine, crystal violet,trinitrobenzoic acid, 1,3,5-trinitrobenzene, and acid fuchsine.
 5. Aprocess for indicating the presence of an adhesive on a substratecomprising the steps of:(a) providing: a sprayable, self-fading coloradhesive comprising the following four components:(i) clear or slightlycolored adhesive dissolved in an organic solvent, (ii) basic materialwhich readily volatilizes at ambient temperatures, (iii) acid-baseindicator which is colored in a basic environment and fades to clearupon drying, and (iv) spraying agent; (b) spraying said adhesive onto asubstrate to provide a colored layer of adhesive; and (c) allowing theadhesive to dry whereupon the color of the adhesive subsequently fades.